UNDERGROUND

route, flying by Venus once and Earth twice in a gravitational slingshot effort to get up enough momentum to reach Jupiter.

NASA's finest minds had wrestled for years with the problem of exactly how to get the probe across the solar system. Solar power was one option. But if Jupiter was a long way from Earth, it was even further from the Sun — 778.3 million kilometres to be exact. Galileo would need ridiculously large solar panels to generate enough power for its instruments at such a distance from the Sun. In the end, NASA's engineers decided on a tried if not true earthly energy source: nuclear power.

Nuclear power was perfect for space, a giant void free of human life which could play host to a bit of radioactive pluto- nium 238 dioxide. The plutonium was compact for the amount of energy it gave off — and it lasted a long time. It seemed logical enough. Pop just under 24 kilograms of plutonium in a lead box, let it heat up through its own decay, generate elec- tricity for the probe's instruments, and presto! Galileo would be on its way to investigate Jupiter.

American anti-nuclear activists didn't quite see it that way. They figured what goes up might come down. And they didn't much like the idea of plutonium rain. NASA assured them Galileo's power pack was quite safe. The agency spent about $50 million on tests which supposedly proved the probe's gen- erators were very safe. They would survive intact in the face of any number of terrible explosions, mishaps and accidents. NASA told journalists that the odds of a plutonium release due to 'inadvertent atmospheric re-entry' were 1 in 2 million. The likelihood of a plutonium radiation leak as a result of a launch disaster was a reassuring 1 in 2700.

The activists weren't having a bar of it. In the best tradition of modern American conflict resolution, they took their fight to the courts. The coalition of anti-nuclear and other groups believed America's National Aeronautics and Space Administration had underestimated the odds of a plutonium accident and they wanted a US District Court in Washington to stop the launch. The injunction application went in, and the stakes went up. The